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Suunto EON Steel User Guide - 2.5

Decompression dives

When on a decompression (deco) dive you exceed the no-decompression limit, Suunto EON Steel provides the decompression information required for ascent. Ascent information is always presented with two values:

  • ceiling: depth that you should not go above
  • asc. time: optimum ascent time in minutes to surface with given gases

NEVER ASCEND ABOVE THE CEILING! You must not ascend above the ceiling during your decompression. In order to avoid doing so by accident, you should stay somewhat below the ceiling.

On a decompression dive, there could be three kinds of stops:

  • Safety stop: this is a recommended three-minute stop for every dive over 10 m (33 ft).
  • Deepstop: this is a recommended stop when you dive deeper than 20 m (66 ft).
  • Decompression stop: this is a compulsory stop on your decompression dive that is for your safety, preventing decompression sickness.

In Dive settings » Parameters, you can

  • turn deepstops on or off (it is on by default)
  • adjust the safety stop time to be 3, 4 or 5 minutes (default is 3 minutes)
  • set last stop depth to 3.0 m or 6.0 m (default is 3.0 m)

The following illustration shows a decompression dive where the ceiling is at 17.7 m (58 ft):

deco dive steel

From bottom to top you see the following in the above image:

  1. There is a decompression window (Deco window) that is the distance between the decompression ceiling (Deco ceiling) plus 3.0 m (9.8 ft) and the decompression ceiling. So the decompression window in this example is between 20.7 m (68 ft) and 17.7 m (58 ft). This is the area where decompression takes place. The closer to the ceiling you stay, the more optimal the decompression time is.

    When you ascend close to the ceiling depth and enter the decompression window area, two arrows appear in front of the depth number. The downward and upward pointing white arrows indicate that you are within the deco window.

  2. If you ascend above the ceiling depth, there is still a safe margin area, equaling to ceiling depth minus 0.6 m (2 ft). So in this example, it is between 17.7 m (58 ft) and 17.1 m (56 ft). In this safe margin area, decompression calculation still continues, but you are advised to go down below ceiling depth. This is indicated by the ceiling depth number turning yellow with a downward pointing yellow arrow in front of the depth number.

  3. If you go above the safe margin area, the decompression calculation is paused until you go back down below this limit. An audible alarm and a red downward arrow in front of the depth number indicate unsafe decompression.

    If you ignore the alarm and stay above the safe margin for three minutes, Suunto EON Steel locks the algorithm calculation, and decompression information will not be available anymore on the dive. See Algorithm lock.

Decompression display examples

Below is a typical decompression dive view showing ascent time and the first required deepstop at 20.3 meters:


Suunto EON Steel shows the ceiling value always from the deepest of these stops. Deepstop and safety stop ceilings are always at constant depth when you are at the stop. Safety stop and decompression stop times are counted down in minutes, deep stop time is shown in minutes and seconds.

In the below display, the deepstop ceiling depth is set to 10.8 m and the diver is currently at 11.1 m. White arrows beside the depth value show the diver is inside the deepstop window. 1' 18 is shown in yellow as the time for an optional stop:

deeptsop steel white arrows

The below display shows that the ceiling depth is set to 3.0 m and the diver is at 3.7 m. The white arrows indicate again that the diver is inside the decompression window. 3' 09 is shown in red as the time for a compulsory stop:

ceiling 3 red steel

The next example shows that the diver is at 2.4 m (ceiling depth is still set to 3.0 m), so inside the decompression window but above the limit. A yellow downward pointing arrow indicates the diver is recommended to descend to be at optimal depth. The optimal depth (the ceiling depth) of 3.0 m is displayed in yellow:

safety stop yellow steel

The below display shows that the ceiling depth is set to 3.0 m and the diver is at 2.3 m. The diver is outside of the decompression window and must descend. A red arrow and an alarm sound prompt the diver to dive deeper and the ceiling depth is indicated in red. Instead of the time, "- -" is displayed as the diver is outside of the decompression window.

stop red steel


If the ceiling is broken for more than 3 minutes, the decompression algorithm gets locked.

Below is an example of what Suunto EON Steel displays during a deepstop:


With decompression stops, in the continuous ascent mode the ceiling is constantly decreasing while you are near the ceiling depth, providing continuous decompression with optimum ascent time. While in the stepped ascent mode, the ceiling is the same for a specific time and then moves upwards 3 m (10 ft) at a time.


It is always recommended to keep close to the decompression ceiling when ascending.

Ascent time is always the minimum time needed to reach the surface. It includes:

  • Time required for deepstops
  • Ascent time from depth at 10.0 m (32.8 ft) per minute
  • Time needed for decompression

When diving with multiple gases, remember that the ascent time is always calculated with the assumption that you use all the gases found in the Gases menu. Always check that you have only the gases for your current planned dive defined before you dive. Remove the gases that are not available for the dive.


YOUR ACTUAL ASCENT TIME MAY BE LONGER THAN DISPLAYED BY THE DIVE COMPUTER! The ascent time will increase if you: (1) remain at depth, (2) ascend slower than 10 m/min (33 ft/min), (3) make your decompression stop deeper than at the ceiling, and/or (4) forget to change the used gas mixture. These factors might also increase the amount of breathing gas required to reach the surface.

Last stop depth

You can adjust the last stop depth for decompression dives under Dive settings » Parameters » Last stop depth. There are two options 3 and 6 m (10 and 20 ft).

By default, the last stop depth is 3 m (10 ft). This is the recommended last stop depth.


This setting does not affect the ceiling depth on a decompression dive. The last ceiling depth is always 3 m (10 ft).


Consider setting the last stop depth to 6 m (20 ft) when you dive in rough sea conditions and stopping at 3 m is challenging.

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